Fredrickson, J. K.

Heald, S. M.

Jeon, B.-H.

Kukkadapu, R. K.

McKinley, J. P.

Zachara, J. M.

UNT Digital Library

Pacific Northwest National LaboratoryU.S. Department of EnergyApril 18, 2005Biogeochemical Coupling of Fe and TcSpeciation in Subsurface Sediments:Implications to Long-Term Tc ImmobilizationJ.M. Zachara*, J.K. Fredrickson, R.K. Kukkadapu,B.-H. Jeon, S.M. Heald, and J.P. McKinleyPacific Northwest National Laboratory, Richland, WA2Project GoalsCharacterize coupled redox reactions betweenbiogenic Fe(II) and Tc in Hanford and FRC sediments Reactivity of biogenic Fe(II) for Tc(VII) and O2 Reoxidation rate of Tc(IV)O2 Abiotic Biotic Extra thermodynamic and kinetic factorsRigorously characterize reoxidation rates underrelevant conditions “In-situ” precipitates Microaerophilic conditions Water advection Other environmental oxidants3Redox Ladder at pH = 7 and 25° C[Aqueous species at equimolar concentrations, others as noted](10-5 mol/L)(10-5 mol/L)UDC/UO2(c)(10-8 mol/L)TcO4-/TcO2•nH2O(10-8 mol/L)MRB4Solubility of TcO2•2H2OTcO(OH)°2(aq)16,784 pCi/L1,678 pCi/L168 pCi/LConcentration ofTc(IV) fixed bysolubililty atreduction pointDowngradientadsorption of Tc(IV)complexes essentialto reach MCL (900pCi/L)Adsorption behaviorof TcO(OH)2°(aq)unknownMCL900 pCi/L5Influence of NO3- on TcO4- Reduction byBioreduced, Pasteurized FRC Sediment 0 1 2 3 4 5 6 7 8 9 100510152025Control with 5 mM NO3-Bioreduced with 5 mM NO3-Bioreduced with 20 mM NO3-Bioreduced Tc Reduction with NO3Aqueous Tc (0.2 µm filtered ) µMTime, h6Oxidation of Biogenic TcO2•xH2O in SinglePhase Suspensions and in FRC Sediment0 2 4 6 8 10 12 14 16 18 20 22µ02468 aerobic  anaerobic 0 10 20 30 40 50 60 70 80 90 100µ02468101214161820220.5N HCl ext0246810121416  Tc, unreduced   Tc in bioreduced  0.5N HCl ext Fe(II)mM Re-aerationEpisodic oxidation Open system oxidationTime, (d) Time, (d)Aqueous Tc, µmAqueous Tc (0.2 µm) µM 0.5N HCl ext Fe(II) mM7Comparative Oxidation of Tc(IV) in Oak Ridge(FRC) and Hanford (Ringold) Sediments0204060801000 50 100 150 200 250time (days)1230204060801000 10 20 30 40time (days)1234%Tc(IV) oxidized%Tc(IV) oxidizedTime (days) Time (days)FRC/ORNL Ringold/HanfordSediments contain 1 mM of heterogeneously reduced Tc(IV)8Distribution of Tc and Fe in BioreducedFRC Sediment (by XRM)Tc FeBSE of “weathered” particle9Kinetic Pathways for Tc(VII) Reductionand Tc(IV) OxidationReduction (+ Fe(II) or MRB)Tc(VII)O-4(aq)Oxidation (+ O2 or MOB)biologic (MRB)+homogeneousFe(II)aqheterogeneousFe(II)OH Fe(II)aqTc(IV)•  speciation•  physical locationFe(III) oxideTcO4t = kbio[    ] + khomo[    ] + khet1[    ] + khet2[    ]Tc(IV)t = kbio[    ] + khomo[    ] + khet1[    ] + khet2[    ]10Homogeneous Reduction of Tc(VII)O4-by Fe(II)aq (Tc)Time, Day0 10 20 30Dild T(VII) µM02468101214 pH 7.0, 0.05mM Fe(II) pH 7.0, 0.1mM Fe(II) pH 7.0, 0.2mM Fe(II) pH 7.0, 0.4mM Fe(II) pH 7.0, 0.8mM Fe(II) 11Homogeneous Reduction of Tc(VII)O4-by Fe(II)aq (Fe)Time, Day0 10 20 30Dild F(II) M0.00.20.40.60.81.0pH 7.0, 0.05mM Fe(II) pH 7.0, 0.1mM Fe(II) pH 7.0, 0.2mM Fe(II) pH 7.0, 0.4mM Fe(II) pH 7.0, 0.8mM Fe(II) TcO4- + 357Fe2+ + [9 + (2-X)H2O] = TcO2•xH2O + Fe(OH)3 + 5H+12Transmission Electron Microscopy ofHomogeneous Fe/Tc Precipitates (pH = 7.0)10 nmd = 3.76A139696.59797.59898.59999.5100100.5-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12a) RT9898.298.498.698.89999.299.499.699.8100100.2-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12b) 77 K97.5098.0098.5099.0099.50100.00100.50-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12c) 12 K9092949698100102-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12a) RT889092949698100102-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12b) 77 K949596979899100101-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12c) 12 K97.59898.59999.5100100.5-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12a) RT99.399.499.599.699.799.899.9100100.1-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12b) 77 KpH 6.8 pH 8.0pH 7.0Velocity (mm/s)% Transmisson57Fe Mössbauer Spectra of Homogeneous Fe/TcPrecipitates (Tc4+ substituted Magnetite?)14Heterogeneous Tc Reduction by Fe(III)Oxides (Tc)Time, Day0 2 4 6 8 10µ051015pH 7.0, 3.0g/L Goethite pH 7.0, 9.0g/L Hematite pH 5.6, 4.5g/L Hematite Time, Day0 2 4 6 8 10µ05101520250.12mM Fe(II), 4.5g/L Hematite 0.23mM Fe(II), 9.0g/L Hematite 0.12mM Fe(II), 1.5g/L Goethite 0.23mM Fe(II), 3.0g/L Goethite Without Fe(II) With Fe(II)15Heterogeneous Tc Reduction by Fe(III)Oxides (Fe)Time, Day-6 -4 -2 0 2 4 6 8 100.00.10.20.30.12mM Fe(II), 4.5g/L Hematite 0.23mM Fe(II), 9.0g/L Hematite 0.12mM Fe(II), 1.5g/L Goethite 0.23mM Fe(II), 3.0g/L Goethite Time, Day-6 -4 -2 0 2 4 6 8 100.00.10.20.30.12mM Fe(II), 4.5g/L Hematite 0.23mM Fe(II), 9.0g/L Hematite 0.12mM Fe(II), 1.5g/L Goethite 0.23mM Fe(II), 3.0g/L Goethite Fe(II)TOT Fe(II)aqSolid added Tc(VII) added Solid addedTc(VII) added16Tc-XAFS of Homogeneous and HeterogeneousPrecipitated Tc(IV)-1.501.50 2 4 6 8 10 12 14k (Å-1)k2 (k)TcRingold120_mergeTcFRC60_mergeTcDCB_FRC1_mergeTcDCB_FRC2_mergeSediments and layer silicates (FRC) Fe/Tc precipitates and Fe(III) oxides-1.501.50 2 4 6 8 10 12 14k (Å-1)k2 (k)Tc512_mergeTcMo583_mergeTcHematite_pips_mergeTcGoethite_pips_merge17XAFS Modeling of Homogeneous andHeterogeneous Precipitated Tc(IV)-8-6-4-2024680 2 4 6 8 10 12 14q (Å-1)q2 (q)datafit-1.501.50 2 4 6 8 10 12 14q (Å-1)q2 (q)datafitHeterogeneous LLSTcO2•H2O chains [6 Tc-O at 2.02 and 2 Tc-Tc at 2.5]Heterogeneous oxideAdsorbed/coprecipitated Tc(IV)[6 Tc-O at 2.00, 1 Tc-Fe at 2.54, 2 Tc-O at 3.0]18Oxidation of Homogeneous and HeterogeneousPrecipitated Tc(IV)024681012140 50 100 150 200 250Time, hrs% Tc(IV) oxidized58942-6-Tc/pH 6.858942-6-Tc/pH 7.058942-6-Tc/pH 8.005101520253035400 20 40 60 80 100 120 140 160Time, hrs% Tc(IV) oxidized58155-149-Tc/goethite58155-149-Tc/hematite58155-149-Tc/DCB-FRC-158155-149-Tc/DCB-FRC-2Homogeneous Heterogeneous19OMPeriplasmBiogenic TcO2Oxidation of Biogenic TcO2•xH2O0204060801000 50 100 150 200 25058942-12-Tc/MR-1A 58942-12-Tc/MR-1B 58942-12-Tc/MR-1C58942-12-Tc/GSP-A 58942-12-Tc/GSP-B 58942-12-Tc/GSP-C 58942-12-Tc/CN32 58942-12-Tc/Abiotic 58942-12-Tc/TcO4 cc% Tc(IV) oxidizedTime, hrs20ConclusionsReductionRate:  hetero (oxide) >> hetero (LLS) >> homo Rate increases with pH and Fe(II) Three speciation forms observed Outer sphere Fe(II) on LLS not reactiveOxidationRate:  cell associated > hetero (oxide)  hetero(LLS) > homo Highly variable rates and extent Tc reduction mechanism/speciation pH Fe(II) concentration/speciation O2 concentration and flux Aging effect Physiologic effects unexploredbiotic21TcO4- and NaNO3 Beneath LeakedHanford HLW Tank SX-10899Tc log (pCurie/L)4 5 6 7 8 9Depth belo1020304050TcO4-mol/L0 2 4 6 8 10 12 14 16 18Dth B1020304050Na(mol/L) vs Depth(m) NO3(mol/L) vs Depth(m) NaNO322Miscible Displacement of 99Tc(VII)O4- FromContaminated Hanford SedimentPORE VOLUME V/V00 1 2 3 4 5 6 7 8 9 10T tti µl L024681012141618SF 720 hoursPORE VOLUME  V/V07.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.00.000.020.040.06Tc concentration µmol L-1SF 720 hours

Biogeochemical Coupling of Fe and Tc Speciation in Subsurface Sediments: Implications to Long-Term Tc Immobilization

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Biogeochemical Coupling of Fe and Tc Speciation in Subsurface Sediments: Implications to Long-Term Tc Immobilization

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